1. Field of the Invention
The present invention relates to an optical pickup apparatus for writing or reading information signals on or from an optical disc as an optical recording medium and a signal recording and/or reproducing apparatus equipped with this optical pickup apparatus for recording or reproducing information signals on or from an optical disc.
2. Description of Related Art
Conventionally, an optical pickup apparatus for writing or reading information signals on or from an optical disc as an optical recording medium has been proposed, and a signal recording and/or reproducing apparatus equipped with this optical pickup apparatus for recording or reproducing information signals on or from an optical disc has been proposed.
With respect to such an optical pickup apparatus, it is demanded that it support optical discs having a higher recording density for information signals for which it is necessary that the wavelength of the light emitted by the laser diode serving as a light source be shortened and numerical apertures (NA) of the objective lens be increased.
For example, according to an optical pickup apparatus that is configured using a high numerical aperture objective lens (an optical pickup apparatus for a high density phase change optical disc), which has been proposed in recent years, as shown in FIG. 9, a light beam emitted from a laser diode 101 is shaped into a parallel beam by a collimator lens 102, and is further shaped by an anamorphic prism 103 into a light beam whose light intensity profiles in two orthogonal directions (the light intensity profile of the cross section of the light beam) are substantially equal before entering a beam splitter 104.
The light beam, which has passed through the beam splitter 104, passes through a beam expander for correcting spherical aberration including a concave lens 105 and a convex lens 106, is deflected in a direction normal to an optical disc 109 by a reflecting mirror 107 and enters an objective lens 108. The light beam entering the objective lens 108 is focused on a signal recording surface of the optical disc 109 as a minute light spot by this objective lens 108.
In addition, in order to maintain the intensity of the emitted light from the laser diode 101 constant, the light beam reflected by the beam splitter 104 is received by an optical detector 110 so as to feedback-control the light emission output of the laser diode 101 based on the output of this optical detector 110.
The light beam reflected by the signal recording surface of the optical disc 109 passes through the objective lens 108 again, is deflected by the reflecting mirror 107, passes through the convex lens 106 and the concave lens 105 of the beam expander, and returns to the beam splitter 104. At this beam splitter 104, the reflected light from the optical disc 109 is reflected and deflected, and is focused, by a condenser 111, on a light receiving surface of an optical detector 112.
Optical elements constituting such an optical system are provided in an optical block 113. As shown in FIG. 9 with arrow T, this optical block 113 is operated movably in a tracking direction, where the objective lens 108 moves towards or away from a spindle shaft 114 supporting a center portion of the optical disc 109.
In such an optical pickup apparatus that supports optical discs with a high recording density, providing the anamorphic prism 103 and the beam expander makes the configuration of the optical system complicated and may cause the apparatus to become larger.
Further, in this optical pickup apparatus, because the entire optical block 113 has to be moved in order to access a given information track, quick activation and stopping of the apparatus cannot be achieved and there is the risk that the time taken to access a desired information track becomes longer.
As such, in recent years, for use in a signal recording and/or reproducing apparatus (i.e., a signal recording and/or reproducing apparatus for high density phase change optical discs), there has been proposed an optical pickup apparatus having a configuration in which, as shown in FIG. 10, the laser diode 101 as the light source, the beam splitter 104, and the optical detectors 110 and 112 and the like are provided in a fixed optical block 115, and only optical components such as the objective lens 108 and the reflecting mirror 107 are provided in the movable optical block 113.
According to this optical pickup apparatus, in the fixed optical block 115, a light beam that is emitted from the laser diode 101 is shaped into a parallel light beam by the collimator lens 102, and is further shaped by the anamorphic prism 103 into a light beam whose light intensity profiles in two orthogonal directions (the light intensity profile of the cross section of the light beam) are substantially equal before entering the beam splitter 104. In order to maintain the light emission intensity of the laser diode 101 constant, the light beam reflected by the beam splitter 104 is received by the optical detector 110 so as to feedback-control the light emission output of the laser diode 101 based on the output of this optical detector 110.
The light beam that has passed through the beam splitter 104 is emitted from the fixed optical block 115 and enters the movable optical block 113. Then, in this movable optical block 113, the light beam passes through the beam expander for correcting spherical aberration composed of the concave lens 105 and the convex lens 106, is deflected in a direction normal to the optical disc 109 by the reflecting mirror 107, and enters the objective lens 108. The light beam entering the objective lens 108 is focused on the signal recording surface of the optical disc 109 as a minute light spot by this objective lens 108.
The light beam reflected by the signal recording surface of the optical disc 109 passes through the objective lens 108 again, is deflected by the reflecting mirror 107, passes through the convex lens 106 and the concave lens 105 of the beam expander, is emitted from the movable optical block 113 and enters the fixed optical block 115.
In the fixed optical block 115, the reflected light from the optical disc 109 returns to the beam splitter 104. At this beam splitter 104, the reflected light from the optical disc 109 is reflected and deflected, and is focused, by the condenser 111, on the light receiving surface of the optical detector 112.
In this optical pickup apparatus, in order to access a desired track, as shown in FIG. 10 with arrow T, only the movable optical block 113 need be moved in the tracking direction, whereby the objective lens 108 is moved towards or away from the spindle shaft 114 supporting a center portion of the optical disc 109. Therefore, in this optical pickup apparatus, the optical block 113 can be activated and stopped at high speed and it is possible to shorten the time taken to access a desired information track.